The use of genetically altered mice has become a standard biological technique aimed at addressing both the physiologic role and molecular mechanism of action of various peptides. Typically studies of transgenic or knockout mice involve specific studies of the peptide of interest. However, it is increasingly apparent that alterations of peptide expression through transgenic or knockout animals may have unexpected effects. In the case of obesity and Type II diabetes, alterations in molecules regulating body weight and glucose homeostasis may lead to changes in overall energy homeostasis that may result from changes in feeding, changes in energy expenditure or altered hormone sensitivity. These results may be expected or unpredictable, as the targeted peptide may be involved in unknown interactions with other molecules. Hence, in evaluating transgenic or knockout models it is essential that in addition to examining parameters such as body weight and insulin sensitivity it is important to examine energy expenditure and oxygen consumption through calorimetry as well as to properly evaluate patterns of feeding behavior. There are nine investigators involved in research on obesity and diabetes who are actively using close to 50 different genetically engineered mouse models. Many of these models have an obese or lean phenotype, which must involve either changes in feeding or energy expenditure or both. This applications for the CLAMS, if funded, will allow analysis of energy expenditure in these animals and general behavior as well as allow precise monitoring of feeding and drinking. This analysis is essential for understanding the perturbations that lead to obesity and diabetes. Use of this instrument will be integrated with the Animal Core funded by the JDC National Institutes of Health (NIH)-funded Diabetes and Endocrinology Research Center (DERC) (DK 36836) which will be increasingly focused on physiologic and behavioral evaluation of mice.